All publications cited herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Cancer vaccines have the potential to target tumors while sparing normal tissue. There is also renewed interest in immunotherapies for malignancies; the FDA recently approved Provenge®, which will be the first commercially available cancer vaccine for the treatment of a solid tumor (15). It is surprising that Provenge® has been approved for advanced prostate cancer, which is not considered a classic immunoresponsive disease. This suggests that cancer vaccines may be effective for many malignancies, and it is expected that important lesson learned while developing Provenge® will facilitate the development of vaccines for other malignancies.
The mammalian target of rapamycin, mTOR (also known as mechanistic target of rapamycin and FK506 binding protein 12-rapamycin associated protein 1 (FRAP1)), is a protein which in humans is encoded by the FRAP1 gene (1, 2). mTOR is a serine/threonine protein kinase involved in the regulation of protein synthesis, transcription, cell growth, cell proliferation, cell motility, and cell survival (3, 4). mTOR is a pivotal regulator of cell proliferation. mTOR integrates the input from upstream pathways, including mitogens, insulin, and growth factors (such as IGF-1 and IGF-2) (3). In addition, mTOR senses cellular nutrient and energy levels and cellular redox status (5). The mTOR pathway is dysregulated in many human diseases, especially certain cancers (4).
The immunosuppressive effects of mTOR inhibition are well known; mTOR inhibition with rapamycin or one of the rapamycin analogs is part of the standard regimen for immune suppression following organ transplantation. Rapamycin, the prototypic mTOR inhibitor, is a bacterial product that can inhibit mTOR by associating with its intracellular receptor FKBP12 (6, 7). The FKBP12-rapamycin complex binds directly to the FKBP12-Rapamycin Binding (FRB) domain of mTOR (7). Rapamycin is widely used to suppress the immune system and prevent rejection of solid organ transplants. The best characterized immunosuppressive effects of rapamycin are based on its activities against T cells and antigen presenting cells (APCs). In mice, rapamycin causes thymic involution (16) and inhibits T cell development (17, 18), proliferation, and migration (19). When compared to effector T cells, regulatory T (Treg) cells are less sensitive to mTOR inhibition; therefore, the Treg population becomes overrepresented (20). In addition, rapamycin may directly induce Treg formation; mTOR inhibition has been shown to make T cells more sensitive to TGF-β-induced Treg-differentiation (21). Dendritic cells (DCs) have also been described as targets of mTOR inhibition; mTOR inhibitors can suppress DC maturation (22) by interfering with antigen uptake (23). mTOR treated DCs are unable to stimulate effector T cells and may even promote the differentiation of Treg cells (23, 24). Thus, recent reports attributing immune stimulating effects to mTOR inhibition are surprising. These reports show that rapamycin can enhance vaccines targeting bacterial or virus in mouse models (9).
Renal cell carcinoma (RCC) is a classic immunoresponsive tumor. However, an effective cancer vaccine is not available for clinical use. For patients with metastatic RCC, the historical 3-year survival is less than 5% (10). Of all urologic malignancies, RCC has the highest ratio of disease-related deaths to incidence. The standard treatments for metastatic RCC include immune cytokines and small molecule targeted therapies. With targeted therapies, complete responses are rare, occurring in only 1% of patients, and patients with partial responses eventually progress and succumb to the disease (11, 12). In contrast, high dose interleukin-2 (IL2) produces complete responses and durable remissions in 5-10% of patients with metastatic RCC (10, 13, 14, 15). According to certain embodiments and as disclosed herein, the inventors show that immune-based therapies provide treatment of the advanced disease state of RCC and/or melanoma.
CD4 expressing lymphocytes include both helper T cells and regulatory T cells. T helper cells are critical to mounting an adoptive immune response. However, regulatory T cells (Tregs) inhibit the function of cytotoxic T cells and normally function to limit an immune response. Therefore, the inventors evaluated CD4 depletion as a strategy for removing Treg activity. Although only a small fraction of CD4 lymphocytes are Treg cells, CD4 depletion remains an effective approach for depleting Treg activity, and importantly, it has the potential for rapid translation to clinical use. There are humanized CD4 depleting antibodies being evaluated in clinical trials. However, there is currently no way to specifically target Foxp3 expressing cells in patients. Applicants show that the combination of mTOR inhibition and CD4 depletion has a potent antitumor immune effect, capable of inhibiting the growth of established tumors as well as hematogenous metastasis.